Structural optimization of hydrogen swirl ejector based on multiphase flow simulation

The configuration of a hydrogen ejector directly affects its entrainment performance and overall efficiency in the proton exchange membrane fuel cell (PEMFC) system. Conventional optimization approaches are plagued by disadvantages such as ineffectiveness and high computational complexity. However, the adjoint method can effectively address these limitations. This work implemented the adjoint method to enhance the performance of a three-dimensional swirl hydrogen ejector. This study simulated the actual situation of internal multiple-field coupling, including the mixture of hydrogen, nitrogen, and water vapor, water vapor condensation, and liquid water distribution. The adjoint method and response surface approaches were employed to investigate the impact of fluid composition on ejector performance and optimization. The best optimization occurred when the nitrogen content was approximately 2%, and relative humidity was 30-60%. After implementing adjoint optimization, the entrainment ratio of the ejector increased by 4.58%, while the hydrogen recirculation ratio witnessed a 4.55% enhancement. Furthermore, the transition of water vapor to liquid in the ejector was decelerated, resulting in a substantial 84.42% reduction in the mass flow rate of liquid water exiting the ejector. The reduction of condensate reduces the occurrence of water flooding in fuel cells, thereby improving the operational efficiency of the system. The effectiveness and practicality of the adjoint method in optimizing ejector structures were demonstrated through a comparison with the parameter analysis method.